There is conventionally known a secondary battery including a negative electrode sheet having a negative active material layer containing negative active material particles. As the negative active material particles, known are particles made of carbon such as graphite. It is also known that the negative active material layer is made of two kinds of negative active material particles made of carbon. For example, Patent Document 1 listed below discloses forming a negative active material layer from negative active material particles made of low-temperature calcined or baked carbon obtained in such a manner that volatile organic substances or the like obtained from carbon and petroleum pitch are calcined at a temperature of 1000° C. or less, and negative active material particles made of fibrous carbon material or graphite (see claims and others of Patent Document 1). It is disclosed that the negative active material layer formed as above enables improvement of a capacity retention rate in a cycle test in which charge and discharge at a low rate (e.g., a current value of 1 C) are repeated in a wide SOC range.
Patent Document 2 for example discloses forming a negative active material layer from negative active material particles made of graphitizable carbon material obtained by calcining or baking petroleum pitch, polyacene, polysiloxane, etc. at 800° C. to 1000° C. and negative active material particles made of non-graphitizable carbon material obtained by calcining or baking petroleum pitch, polyacene, polysiloxane, etc. at 500° C. to 800° C. (see claims and others of Patent Document 2). It is disclosed that the negative active material layer formed as above enables suppression of deterioration in the capacity of a secondary battery and improvement of a capacity retention rate in a cycle test in which charge and discharge at a low rate (e.g., a current value of 1 C) are repeated in a wide SOC range.